Note: Descriptions are shown in the official language in which they were submitted.
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INTERRUPTED POWER HOT WIRE GAS IGNITION CONTROL SYSTEM
BACKGROUND OF THE INVENTION
In recent years the cost and availability of gas as a
fuel has forced drastic conservation measures in its use. In the
pas., standing pilots have been used extensively in gas fired
equipment. A standing pilot is nothing more than a pilot burner
that is continuously lit and which is monitored by a bulb and
fill, a thermocouple, or similar safety device. The standing pi-
lot has been used because of its very low cost and its reliabili-
ty.
The standing pilot utilizes gas continuously and,therefore, has been deemed to be an inefficient and expensive use
of this fuel. In many states the standing pilot has been
legislated out of existence. In order to meet the legislative
and economic demands for a better pilot system, a number of other
approaches have been used. Typical of these other approaches are
spark ignition systems which light a pilot and then allow a main
burner to become energized. The spark ignition systems have nu-
merous problems including the generation of radio frequency in-
terference and audible noise which make them objectionable. In
addition to spark ignition systems, hot wire ignitors have been
used for many years. Hot wire ignitors have proved unreliable
due to the deterioration of the ignitor itself, thereby causing
high maintenance costs in replacing the ignitor.
Hot wire or hot surface type ignitors have been used in
intermittent applications where a pilot burner is ignited and
then the hot wire is deenergized to remove the potential on the
wire so as to improve the ignitor's life. Ceramic types of nega-
tive temperature coefficient resistors have come into use to
replace wires. Negative temperature coefficient ceramic resis-
tors can be energized to generate ignition temperatures and with-
stand the operating conditions in a superior and more economical
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fashion than other types of hot wires. While there are some
physical differences between an actual hot wire and a ceramic re-
sistance type device, they generally both have been referred to
as hot wire type devices. The negative temperature coefficient
resistors can be used in systems where the resistance element
provides for both an ignition and monitoring function. In some
systems it has been common to use a negative temperature coeffi-
cient resistor-ignitor element for ignition purposes, and then
monitor the resistance of that element as a means of detecting
flame. This type of system is theoretically workable, but in
practice the life of the resistor-ignitor element is so limited
that it limits its use in a practical burner ignition arrange-
ment.
The deficiencies of the actual hot wire type devices
15. and the negative temperature coefficient resistor-ignitor ele-
ments which have been used can only be overcome if a way can be
found to lengthen the life of the ignition element itself.
SUMMARY OF TE~E INVENTION
The present invention is directed to a system for the
control of power to an ignition element. The power to the igni-
tor is supplied through a series combination of a normally closed
; relay contact and a resistor. AS the ignitor approaches the ig-
nition temperature for gas, its resistance decreases measurably.
This decrease in resistance allows for a reduction in a voltage
drop across the ignitor element with a related increase in volt-
age appearing across the series resistance. This increase in
voltage lS used to control a switching circuit that operates the
pilot valve section of a valve means. The pilot valve section is
opened and ignition occurs at the ignitor element.
In prior art devices the ignitor element would also act
as a sensor and therefore would have to be kept energized. In
the present system a separate flame detector is mounted adjacent
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the burner and detects the presence or absence of flame. Whenflame appears, the flame detector means operates through a flame
responsive circuit means to control a second switching arrange-
ment. This second switching arrangement i5 typically a solid
state switch means to control a relay. The relay has a pair of
contacts. The first contact is the normally closed contact that
is in the series energizing circuit for the ignitor element. The
second contact is a normally open contact that is in turn closed
upon the detection of flame. The closing of the normally open
contact provides power to the main valve section. The closing of
this contact also completes a holding circuit for the pilot valve
device along with the interruption of power to the ignitor ele-
ment. This allows the ignitor element to be energized only
during the ignition phase of operation and ensures a long life
for the ignitor element.
The present invention basically entails the use of a
hot wire ignitor system for the initiation of the pilot flame
while utilizing a flame detector means that is separate from the
ignitor to maintain the operation of the pilot and burner, while
at the same time deenergizing the hot wire ignitor element to im-
prove its life and reliability.
In accordance with the present invention there is
provided an interrupted power hot wire gas ignition control sys-
tem adapted to control a burner having gas valve means incor-
porating a pilot valve and a main valve, including: a negative
temperature coefficient resistor-ignitor element which when
energized from a potential changes in resistance value as the
resistor-ignitor element heats to an ignition temperature with
said element mounted at said burner; a series ignition circuit
including a normally closed relay contact, a resistor, and said
resistor-ignitor element with said ignition circuit adapted to
be connected to a source of potential upon operation of said
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burner; switch means connected to energize said pilot valve;
switch control circuit means connected to said resistor to
control said switch means, and wherein said switch means is
nonconductive when said resistor-ignition element is cold,
and further wherein said switch means is conductive to energize
said pilot valve when said resistor-ignition element is at a
gas ignition temperature; flame detector means mounted at said
burner to detect the presence of a flame when said pilot valve
has opened with said resistor-ignitor element at said gas
ignition temperature; flame responsive circuit means having
an input connected to said flame detector means, and said flame
responsive circuit means having switched output means, said
switched output means including a relay having a normally open
relay contact, and further including said normally closed relay
contact; said normally open relay contact connected to said main
valve to allow said normally open relay contact when closed to
energiæe said main valve; and impedance means including a diode
connecting said pilot valve to said normally open relay contact;
said relay being energized upon the sensing of flame at said
burner by said flame detector means with said normally closed
relay contact becoming open circuited to remove power from said
resistor-ignitor element while said normally open relay contact
becomes closed circuited to maintain said pilot valve energized
through said impedance means, and to also energize said main
valve.
BRIEF DESCRIPTION OF THE DRAWINGS
The single figure is a schematic diagram of a complete
ignition control:.system~
DFSCRIPTION OF THE PREFERRED E BODIMENT
The single schematic diagram disclosed is a complete
interrupted power hot wire gas igni-tion control system. The term
hot wire has been used in the present specification as a generic
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term for any type of negative temperature coef:Eicient
resistor-ignitor element whether it be in fact a wire or a ceram-
ic type of ignitor element. The early hot wire ignitor elements
were in fact nickel-chromium type wires and these ignitors have
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utility in certain types of applications. In more recent years a
ceramic type of negative temperature coefficient resistor-ignitor
element has been developed for use in gas ignitionO Regardless
of which type of unit is used, the term hot wire gas ignitor will
be used throughout the present description as generic to this
general class of ignitor elements.
A pair of line voltage terminals 10 and 11 are provided
that are connected to a primary winding 12 of a transformer
generally disclosed at 13 which further has a low voltage winding
14. The winding 14 is connected through a switch 15 to a diode
bridge generally disclosed at 16. The bridge has a relay means
disclosed at 20 which includes a relay coil 21 and a parallel ca-
pacitor 22 that ensures proper operation of the relay means 20.
The relay means 20 further has a mechanical coupling 23 to a
normally open contact 24. The relay contact 24 is connected by a
conductor 25 to the line voltage terminal 10. The transformer
means 13 and the switch 15 along with the bridge 16 and the relay
means 20 allows for low voltage operation of the contact 24 which
in turn operates in a line voltage environment. The switch 15
typically would be a thermostat in a residential installation and
would be operated from a 24 volt secondary 14 in a conventional
manner. The contacts 24 of the relay means 20 could be replaced
by a line voltage switch that is either manually operated or
thermostatically operated if that is desired. The only essential
element is that a means of connecting the terminals 10 and 11 to
a pair of conductors 2~ and 27 be provided so that line voltage
is provided between conductors 26 and 27. The conductor 27 is
disclosed as grounded at 28 in a conventional manner.
A flame detector means is generally disclosed at 30 as
a flame rectification type in which a portion of the device is
grounded at 28, and the other portion of the device at 31 is
connected through a pair of resistors 32 and 33 to the conductor
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26. This forms an input circuit for a flame responsive cixcuit
means disclosed at 29. As is well known, a flame rectification
system operates on the principle that when an alternating current
is applied across a flame, the flame allows conduction of a
greater magnitude in one direction than in the other of the
applied alternating current voltage. This resul~s in what ap-
pears to be a rectified flame conducted current, and this princi-
ple allows for the generation of a voltage across the resistor 33
that is a function of whether a flame exists at the flame detec-
tor means 30 or not. The voltage across the resistor 33 isprovided at a junction 34 to a network made up of a capacitor 35,
a resistor 36, a further resistor 37, and a capacitor 38. The
voltage across the capacitor 38 is stabilized by a ~ener diode 40
and is applied through a resistor 41 to a gate 42 of a field ef-
fect transistor 43. The voltage therefore that appears at the
junction 34 is used to control the field effect transistor 43 by
applying a voltage at the gate 42 that is capable of causing the
field effect transistor 43 to either be a substantially open cir-
cuit or a substantially closed circuit.
The voltage across the field effect transistor 43 is
; supplied at a conductor 44 to a parallel combination of a diode
45 and a resistor 46. The resistor 46 is connected to a further
resistor 47 that is connected to the ground conductor 27. The
voltage that is divided between the resistors 46 and 47 is
supplied at a conductor 44 to a gate 50 of a silicon controlled
rectifier 51. The silicon controlled rectifier 51 is connected
by a conductor 52 to the conductor 26. The arrangement described
to this point is a flame detector means 30 and a flame responsive
circuit means 29 which has an input 34 that is connected to the
flame detector means 30 and has a switched output means in the
form of the silicon controlled rectifier 51 along with a relay
means disclosed at 54. The relay means 54 includes a relay coil
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55 that has a stabilizing capacitor 56 and a pair of contacts 60
and 61. The contact 60 is a normally open contact, while the
contact 61 is a normally closed contact. The contacts 60 and 61
are mechanically lin~ed at 62 to the relay means 5~. The relay
means 54 is energized by connection between the silicon
con~rolled rectifier 51 and a resistor 63 that connects the relay
coil 55 to the ground conductor 27.
The normally closed relay contact 61 is connected to
the power conductor 26 and to a fuse 65 along with a resistor 66
and a hot wire gas ignition element 67 that is a negative temper-
ature coefficient resistor-ignitor element, preferably of the ce-
ramic type. As was previously mentioned the particular type of
resistor-ignitor element 67 is not material. The normally closed
contact 61, the fuse 65, the resistor 66, and the
resistor-ignitor element 67 are connected in a series circuit
across the power conductors 26 and 27. Since the
resistor-ignitor element 67 is a negative temperature coefficient
element, it will become apparent that as current flows through
the series circuit that the voltage that appears across the
resistor-ignitor element 67 decreases and a voltage increases
across the resistor 66. This function becomes important in the
operation of the system and will be described after the entire
circuit has been defined.
The resistor 66 acts as an input to a switch means
generally disclosed at 70. The switch means 70 includes a sili-
con controlled rectifier disclosed at 71 which has a gate 72, an
anode 73, and a cathode connection 74. The cathode 74 is
connected to the gate 72 by a parallel combination of a diode 75
and a resistor 76 which act as gating elements for the silicon
controlled rectifier 71. Connected across the resistor 76 is a
bilateral switch 77 and a capacitor 78. The bilateral switch 77
is used to allow a charge to build on the capacitor 78, in a man-
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` ner that will be seen. A connection between the bilateral switch77 and the capacitor 78 at 80 is connected through a resistor 81
and a diode 82 so that the capacitor 78 is connected across the
resistor 66. A voltage appearing across the resistor 66 charges
of the capacitor 78 until the bilateral switch 77 allows dis-
charge of the capacitor 78 through the resistor 76. This
provides a gating potential at the gate 72 of the silicon
controlled rectifier 71. This switch means, that is the switch
means 70, is connected to a terminal 83 that in turn is connected
to a pilot valve 84 that has a further terminal 85 connected to
the ground conductor 27. The pilot valve 84 is operated with a
main valve 86 that has a pair of terminals 87 and 88 to connect
the main valve 86 in the circuit. Each of the valves 84 and 86
is paralleled by a diode 90 and 91 to ensure proper operation of
the valve during alternate half cycles of the applied alternating
current between the terminals 10 and 11. The pilot valve 84 and
the main valve 86 are mechanically arranged so that the pilot
valve 84 must be open to supply gas to a pilot burner before the
main valve 85 will open. This is a standard type of valve
structure. It will be noted that the pilot valve 84 is connected
to the silicon controlled rectifier 71, which in turn connects it
to a point 92 which effectively is connected to the conductor 26
through the fuse 65 and the normally closed relay contact 61.
The operation of the switch means 70 will clearly energize the
valve 84, and the manner in which it is operated will be
described after the balance of the circuit has been disclosed.
An impedance means 93 is disclosed including a diode 94
and a resistor 95 which is connected from the anode 73 of the
silicon controlled rectifier 71 to a junction 96 which is between
a diode 97 and the normally open relay contact 60. The impedance
means 93 is used to maintain the operation of the pilot valve 84
when the circuit is in operation.
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OPlERATION
A brief explanation of operation is provided and is
believed sufficient for this circuit. When the thermostat or
switch 15 is closed, the relay contact 24 closes applying power
between the conductors 26 and 27. A series circuit including the
normally closed relay contact 61, the fuse 65, the resistor 66,
and the resistor-ignitor element 67 is completed. Initially most
of the voltage is dropped across the resistor-ignitor element 67.
As the resistor-ignitor element 67 increases towards an ignition
temperature, the voltage across it drops and the voltage across
the resistor 66 increases. When the voltage across resistor 66
increases sufficiently to break down the bilateral switch 77, the
silicon controlled rectifier conducts energizing the pilot valve
84. This introduces gas' to the hot resistor-ignitor element 67
where ignition then occurs and a pilot flame then is established.
The pilot flame is sensed by the rectification flame
sensing detector means 30, and a voltage is supplied at the junc-
tion 34 for the flame responsive circuit means 29 thereby causing
the silicon controlled rectifier 51 to conduct. This is accom-
plished by cutting off the conduction in the field effect tran-
sistor 43 and allowing the voltage developed in the voltage
divider 46 and 47 to apply voltage at the gate 50 of the silicon
controlled rectifier 51 to pull in the relay means 54. When the
relay 54 is energized, the normally open relay contact 60 closes,
while the normally closed relay contact 61 opens. This operation
provides a direct energizing path through the contact 60 and
diode 97 to the main valve 86 while opening the series circuit in
which the normally closed relay contact 61 has been supplying
power to the resistor-ignitor element 67. The impedance means 93
provides a conduction path at a reduced voltage for the pilot
valve 84 to keep the pilot valve energized once it has been
energized. This is necessary since the silicon controlled recti-
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fier 71 of the switch means 70 is deenergized when the normallyclosed relay contact 61 is opened upon the sensing of flame.
With the arrangement just described a resistor-ignitor
element 67 can be interrupted in its operation and thereby can
provide a device with a very long ignition life. The present
system has been disclosed as operated with a thermosta~ or low
voltage switch 15 to control the line voltage contact 24. The
line voltage contact 24 obviously could be replaced by a line
~ voltage control device and the low voltage section including the
transformer means 13, the bridge 16, the relay means 20 and its
associated circuity could be eliminated. Other variations in the
present circuit could be accomplished by modifying the type of
flame detector used, and the type of electronic or electric
switching used. Since the present circuitry can be modified by
one skilled in the art the inventors wish to be limited in the
scope of their invention to the scope of the appended claims.
